Sperm lengths in mm for D. simulans and D. mauritiana. Variables: Species – sim or maur; Thorax – thorax length as a measure of body size, in an aritrary unit, to be entered as a covariate in analyses. Thorax length should be correlated with SR length but not sperm length.; Sperm1-5 – length in mm for each of 5 sperm measured per male. Average sperm lengths for each male are calculated from the four longest measurements.